: : Its source is a lyric in "The Battle Hymn of the Republic":
"He is trampling out the vintage where the grapes of wrath are stored."
It has to do with righteous anger. Maybe someone else can be more
precise.

: And, as you probably already know, it's the title of a 1939 book:

: From http://www.teachervision.com/lesson-plans/lesson-3540.html

: Life during the Great Depression of the 1930s was extremely difficult
for almost everyone. But for those who had little to begin with,
it created often unbearable circumstances. By 1935, drought and
poor farming practices, especially in Oklahoma, Arkansas, Colorado,
Kansas, and Texas, led to the wind erosion of topsoil. So severe
was this problem that the affected areas of the Great Plains were
labeled the Dust Bowl. At nearly the same time, the development
of the all-purpose tractor enabled large landowners to dispense
with the labor of farmers who were tenants on their land. By the
late '30s, a majority of the approximately 1.8 million tenant farmers
in the South had been evicted from their homes. Many of the displaced
farmers sought work in the "promised land" of California. Eventually,
there were as many as 300,000 migrants in California, several workers
for every available job in the fertile farming valleys of that state.

: In 1936, John Steinbeck conducted research on the people who
had moved to California from Arkansas and Oklahoma; in 1937, he
toured the Dust Bowl and traveled with migrants on their relentless
drive to California. From those experiences he wrote The Grapes
of Wrath, which upon publication in 1939 earned Steinbeck both high
praise (including the Pulitzer Prize) and harsh criticism for its
strong language and sociopolitical implications. The novel continues
to be one of the most highly praised and vehemently criticized pieces
of American literature.